Method for the preparation of a catalyst component for the polymerization of olefins, a polymerization catalyst component produced by the method and use of the same

ABSTRACT

The invention relates to a method for the preparation of a solid procatalyst composition for a catalyst system intended for the polymerization of olefins, wherein a magnesium halide, such as magnesium chloride, is dissolved and/or slurried in a mono-carboxylic acid alkyl ester, such as ethyl acetate, is impregnated into a support material, dried, treated with an organometallic compound or a silicon compound and thereafter with a transition metal compound. The invention also relates to such a procatalyst composition and its use together with a cocatalyst for the polymerization of olefins. According to the invention it has been possible to increase the activity of the catalyst composition by using a silanated support material, such as silanated silica, which is then treated with an organometallic or silicon compound before treatment with a transition metal compound. The silanated silica is preferably a silicon dioxide which has been heat-treated at 1000°-200° and thereafter treated with hexamethyldisilazane and contains 3-6% carbon. The organometallic compound is preferably an aluminum alkyl compound, such as triethylaluminum, and the transition metal compound is preferably titanium tetrachloride.

The invention relates to a method for the preparation of a solidprocatalyst composition for a catalyst system intended for thepolymerization of olefins, method in which support material isimpregnated with magnesium halide and a monocarboxylic acid alkyl esterwhich dissolves the halide, and the impregnated support material isreacted with an organometallic compound or a silicon compound andtreated with a transition metal compound.

For the polymerization of olefins there is commonly used the so-calledZiegler-Natta catalyst system, which comprises a so-called procatalystand a cocatalyst. The procatalyst is based on a compound of a transitionmetal belonging to any of Groups IVB-VIII of the periodic table of theelements, and the cocatalyst is based on an organometallic compound of ametal belonging to any of Groups IA-IIIA of the periodic table of theelements.

In the preparation of heterogeneous polymerization catalysts it isconventional to use as a component improving the polymerization activityof procatalysts a support compound on which the transition metalcompound is deposited. Silica, aluminum oxide, magnesium oxide, titaniumoxide, carbon in various forms, and various types of polymers are commonsupport compounds. Compounds which have proven to be important supportcompounds include magnesium compounds such as alkoxides, hydroxides,hydroxy halides and halides, of which the last-mentioned, specificallymagnesium dichloride, have recently become the most important supportcomponents for procatalyst compositions.

Since magnesium halides in their basic crystal form are not veryeffectively activated by a transition metal compound, their crystalstructure has to be deformed. Conventionally this is done by milling,for example in a ball mill, the result obtained being typically afinely-divided powder with a large specific surface area and with highlydeformed crystal lattices of the particles. When such a powder isactivated to form a procatalyst composition by deposition with atransition metal compound, and is thereafter reduced with anorganometallic compound serving as the cocatalyst, a highly activepolymerization catalyst is obtained.

The conventional method of milling magnesium halide has, however, thedisadvantage that it consumes a very large amount of energy, causes wearand corrosion of the apparatus, and is usable for the preparation of acatalyst only by a cumbersome batch process.

A more novel and more efficient method of decreasing the crystallinityof magnesium halides, and thereby of increasing their ability to becomeactivated by transition metal compounds, is chemical modification.Therein the magnesium halide, an electron donor, and a transition metalcompound are caused, often in a solution, to react with each other toform easily separable procatalyst compositions. U.S. Pat. Nos. 4,124,532and 4,174,429 describe the preparation of such catalytically activecomplexes by reacting at a suitable ratio a magnesium halide and atransition metal compound in an electron donor solvent. The completedcomplex can be separated by evaporation crystallization of the saidsolvent or by doping the complex with a solvent in which it does notdissolve. Since such complex compounds are produced as a result ofspontaneous crystallization, their crystal structure is very regular andtheir activity respectively quite limited. U.S. Pat. Nos. 4,302,566 andEP Application 6110 describe a precursor comprising a magnesium halide,a transition metal compound, and an electron donor. The precursor isformed by precipitation out of an electron donor solution, whereafter itis separated and mixed with an aluminum alkyl which activates it andwith a separate inert support material.

Even in these methods there is not formed a substantially amorphousprocatalyst composition, since the said precursor crystallizesspontaneously in the preparation process and will thereafter notsubstantially change its morphology.

Other patents describe Ziegler-Natta procatalysts on a silica support ora magnesium silicate support, but in them the superior ability ofmagnesium compounds to activate transition metal compounds has not beenexploited. Such patents include: WO 8 802 376, EP 215916, EP 120503, EP91135, EP 80052, EP 55605, EP 43220, EP 20818, U.S. Pat. No. 4,482,687,U.S. Pat. No. 4,383,095, U.S. pat. No. 4,354,009, U.S. Pat. Nos.4,349,648, and 4,359,561.

U.S. Pat. No. 4,670,526 describes a catalyst activation process in whicha divalent magnesium halide together with a Lewis acid, e.g.ethylaluminum chloride, is dissolved in an excess of an electron donor,and the obtained complex is separated from the excess of the electrondonor before a treatment with a titanium or vanadium compound. Thecomplex is alternatively also deposited on silica.

EP Application 267 794A2 describes a catalyst system which is preparedby combining silica or alumina with a magnesium halide and anorganometallic compound. Typically this combining is done by dissolvingthe magnesium halide in an inert solvent; ethyl acetate is alsomentioned as one of these. As regards silica, it is noted that it maycontain small amounts of water, although in the embodiment examples thesilica is calcined. Before the treatment with a transition metalcompound the catalyst component is, according to the embodimentexamples, treated with an electron donor, e.g. vinyl ethoxysilane andtriphenyl phosphite, presumably in order to increase the isotacticity ofthe polypropylene to be polymerized with the catalyst.

The object of the present invention is to provide a procatalystcomposition comprising a support material, a magnesium halide, anorganometallic or silicon compound, and a transition metal compound, andhaving a structure which is maximally amorphous and thus maximallyactive catalytically. The invention also aims at a method for thepreparation of a solid procatalyst composition for a catalyst systemintended for the polymerization of olefins, method which does notrequire a separate step of milling the magnesium halide and in which thetreatment with the transition metal compound takes place at so late apreparation stage that recrystallization of the product and loss ofactivity will no longer occur during its complexing. The inventionfurther aims at finding for the novel procatalyst composition asappropriate use as possible in the polymerization or copolymerization ofolefins, and in particular α-olefins.

According to the invention, these objects have been achieved by amethod, a procatalyst and the use of the same the characteristics ofwhich are given in the independent claims in the accompanying patentclaims.

The invention is thus based on the realization that the change in themorphology of the magnesium halide which is a prerequisite for activityis produced by impregnating a separate, inert silanated support materialwith a magnesium halide and with a monocarboxylic acid alkyl ester whichdissolves the halide. When, after the drying of the solvent, theimpregnated separate silanated support material is reacted with anorganometallic compound, such as an organometallic compound of a metalbelonging to any of Groups IA-IIIA, preferably an aluminumalkylcompound, or with a silicon compound, preferably a halide or alkylhalide compound, the result is a solid silanated support material coatedwith a magnesium halide, and the support is ultimately treated with atransition metal compound. One useful feature of the invention lies inthat the treatment with the transition metal compound takes place laterthan in the conventional homogeneous activation processes of aprocatalyst composition; consequently, the recrystallization of theprocatalyst composition is prohibited and the activity of the mixture isthus retained.

The preparation of the solid procatalyst composition for a catalystsystem intended for the polymerization of olefins thus starts with thedissolving or slurrying of an anhydrous magnesium halide in a suitablemonocarboxylic acid alkyl ester, which serves as the solvent. By themagnesium halide used is meant specifically a magnesium halide in whichthe halogen is chlorine, bromine, iodine, or a mixture of the same. Themost preferred magnesium halide is an anhydrous and dry magnesiumdichloride MgCl₂. The ester used as the solvent is under the processconditions a liquid in which the magnesium compound is partly, orpreferably completely, soluble. It is preferably an alkyl ester of analiphatic carboxylic acid which contains 1-10 carbon atoms, and quiteparticularly ethyl acetate. The dissolving of magnesium halide in theester serving as the solvent is done, when necessary, with the help ofagitation at an elevated temperature.

In the next step, the obtained magnesium halide solution is used forimpregnating a separate silanated support material. An alternativemethod of depositing the magnesium halide on the support is to add themagnesium halide and the solvent simultaneously with the support to forma slurry from which the magnesium halide, upon dissolving, will at leastin the main deposit on the surface of the support.

The inert support is preferably silica, an inorganic oxide of silicon.The particle size of the silica is 10-200 μm, preferably 40-150 μm. Itis preferably selected to that its particle size distribution is asnarrow as possible. In addition, these supports are porous and theirsurface area is preferably over 100 m² /g and voids volume over 1 cm³/g. Untreated silica contains water, which can be removed by a heattreatment, for example at 100°-200°0 C., or for example by distillingthe water azeotropically by means of heptane, or by reacting with anexcess of a silanating reagent. Even if the water present in the silicais removed, the silica will still contain a large quantity of hydroxylgroups. These groups can be removed in many ways. A commonly used methodis to eliminate them by calcination, i.e. by heating in a kiln to atemperature above 200° C., usually in the presence of a nitrogen flow orin dry air. The method is effective but time-consuming. Especially thekilns required for the treatment of large quantities of silica will bevery expensive owing to the special requirements due to the hightemperatures. Therefore it is preferable to use a method in whichseparate calcination is avoided, although the silica can, of course, becalcined before the silanation if it is desired, for example, todecrease the amount of the silanating reagent.

In the present invention it has been observed that by using silanatedsilica as the initial material the disadvantages of kiln drying andcalcination can be avoided, and at the same time better results can beachieved in terms of the properties of the catalyst. By silanating thesilica the hydroxyl groups can be decreased chemically. The silanationcan be carried cut in the same reactor as the other steps of thecatalyst preparation, whereby separate kiln treatments and transfers ofthe silica are avoided.

Before the silanation the water present in the silica can be removed byheating it to a temperature of 100°-200°C., preferably by using a gasflow, for example nitrogen. On a laboratory scale this step can becarried out conveniently even separately in a kiln, because in the caseof small material quantities and low temperatures this is done with verysimple apparatus. Another method of removing the water is to distill thewater azeotropically, for example with the help of heptane. This isadvantageous especially when large amounts of material are involved. Theremaining water and a portion of the hydroxyl groups are next removed bysilanation, in which an organic silicon compound which reacts with thehydroxy groups is added to a slurry of the silica and a suitablehydrocarbon, e.g. heptane. On the other hand, it is also possible thatthe silanation reagent is used in so large a quantity that no heattreatment for the removal of water is necessary.

The said organic silicon compounds are preferably compounds according toformula R_(m) SiX_(4-m), R_(n) Si(OR)_(4-n) or (R₃ Si)₂ NH. R is analkyl group or aryl group having 1-10 carbon atoms, X is a halogen atomsuch as Cl or Br, m=1, 2 or 3, n=0, 1, 2, 3 or 4. Hexamethyldisilazane(HMDS) is especially preferred.

The silanation treatment is carried out by adding, for example, HMDS at5-25% to a hydrocarbon slurry of silica, by agitating for example for0.5-2 hours, and by drying the slurry to produce a freely flowingpowder. The amount of HMDS is dependent on the pre-treatment of thesilica and on its water content. However, the amount is not exact, sinceexcess HMDS is removed during the drying. Also other silanation methodsknown and clear to an expert in the art can be used. The silanation can,of course, also be carried out on a large batch at the same time, fromwhich the desired quantity can be batched for further treatment.

On the basis of a carbon analysis, a silica thus treated typicallycontains carbon 3-6% by weight.

After the silanated support has been impregnated with a magnesium halidesolution or slurry, this being carried out, when necessary, at anelevated temperature, the solvents are evaporated dry, and then theimpregnated support is reacted by treating it with an organometalliccompound of any metal belonging to Groups IA-IIIA, preferably with analuminum alkyl compound or a silicon compound, preferably chloride oralkyl chloride. The product obtained after this treatment can be washedin order to remove the dissolved reaction products, but washing is notnecessary.

The treatment with a transition metal compound is preferably carried outby preparing of the above-mentioned impregnated and dried supportparticles a hydrocarbon slurry to which the transition metal is added,or by adding it directly to the solution after the previous treatment.This treatment can be sped up by using agitation and an elevatedtemperature. The transition metal compound is preferably ahalogen-containing compound of titanium, vanadium, and/or zirconium.Titanium compounds are especially preferred, and titanium tetrachlorideTiCl₄ is the most preferred.

The procatalyst composition obtained after the transition metaltreatment is washed, dried and analyzed. The washing steps are notnecessary; good results have been obtained even when the solvent hasmerely been evaporated off or when the procatalyst has been left in theform of a slurry.

In experiments carried out in connection with the invention it wasobserved surprisingly that the performance of the catalyst prepared inthe manner described above was excellent, specifically with silanatedsilica, and that it was especially well applicable to the polymerizationof ethylene, with a high activity and a high hydrogen and comonomersensitivity. The polymer obtained has a narrow molecular weightdistribution (MWD) and a good morphology for various uses.

EXAMPLE 1

10 g of untreated silica (EP 17MS, Crosfield Chemicals) was slurried in120 ml of heptane in a glass flask. The mixture was heated in a bath toa temperature of 110° C., and water was distilled off azeotropically.Initially the distillate was turbid owing to the water present in theheptane, but gradually the distillate cleared up as the water decreased.Approx. 80 ml of the distillate was collected. 2.26 ml ofhexamethyldisilazane (HMDS) was added to the slurry, and the mixture wasboiled for approx. 1.5 hours.

Ultimately the silanated silica was dried to form a dry powder, by usinga nitrogen flow at 110° C. On the basis of a carbon analysis, thesilanated silica contained carbon 3.34% by weight.

2.5 g of the silanated silica prepared in the above-mentioned manner wasplaced in a flask. On top of the silica there was added a solution whichhad been obtained by dissolving 0.75 g of anhydrous MgCl₂ in 35 ml ofdried ethyl acetate (EA) for 2 hours at a temperature of 80° C. Themixture was agitated at 80° C. for one hour and was dried to produce afreely flowing powder.

Next, the obtained impregnated support was re-slurried in 25 ml of dryheptane, 3.5 ml of a 10 wt. % solution of triethylaluminum in pentanewas added, and the mixture was agitated for one hour at 40° C. Next,0.32 ml of TiCl₄ was added on top of the solution, was agitated for 2hours at 60° C., and dried in a nitrogen flow at 100° C. 3.6 g of aprocatalyst composition was obtained. According to an analysis, theobtained procatalyst composition contained Mg 4.8% by weight, Ti 4.0%,Al 1.5%, Cl 24.4%, and EA 9.5%. The results of the test polymerizationare shown in Table 1.

EXAMPLE 2

2.5 g of silica (Davison 955l) which had been dried for 4 hours at 180°C. in a glass tube while directing nitrogen via the tube was slurried inpentane, and 0.75 ml of hexamethyldisilazane (HMDS) was added. Themixture was agitated for one hour at 50° C. and dried with a nitrogenflow. On top of the treated silica was added a solution which had beenobtained by dissolving 0.75 g of anhydrous MgCl₂ in 33 ml of ethylacetate (EA) dried on molecular screens. The mixture was agitated for 5hours at 80° C. and dried. The obtained product was re-slurried inpentane, and 20.5 ml of a 10% solution of triethylaluminum (TEA) inpentane was added. The mixture was agitated for an hour at 40° C., thesolution was siphoned off, and the product was washed twice withpentane. Then 20 ml of pentane and 0.3 ml of TiCl₄ were added, themixture was agitated for 2 hours at 50° C. and dried. 1.45 g of aprocatalyst composition was obtained which contained Mg 4.1% by weight,Ti 4.1%, Al 1.2% and EA 5.3%.

EXAMPLE 3

2.0 g of silica (Davison 955, calcined at 600° C.) was slurried inpentane and treated with 0.26 ml of HMDS for one hour at 50° C. anddried. 15 ml of ethyl acetate and 0.2 g of anhydrous MgCl₂ were added ontop of the silanated silica, and the mixture was agitated overnight at80° C. After drying, 20 ml of pentane and 2.07 ml of a 10% solution ofTEA were added, the mixture was agitated for one hour at 40° C., and thesolution was siphoned off. The product was re-slurried in pentane, and0.2 ml of TiCl₄ was added, whereafter the mixture was agitated for 2hours at 50° C., and the obtained procatalyst composition was dried. 1.3g of a product was obtained which contained Mg 1.7% by weight, Ti 4.6%,Al 2.0%, and Cl 19.0%, as well as EA 8.4%.

EXAMPLE 4

The procedure was as in the preceding example, but only 0.077 ml ofTiCl₄ was added. The procatalyst composition now contained only 1.9% Ti.

Test polymerization

The test polymerization of ethylene was carried out in each example inthe following manner: into a 3-liter autoclave there was batched 1.8 lof isobutane which had been purified with removers of oxygen andmoisture. 40-80 mg of procatalyst composition was fed in together withaluminum alkyl (TEA, Al/Ti=50-75). The temperature was raised to 90° C.An 0.5-liter pressure vessel, or a bomb, was pressurized to 5 bar withhydrogen, and hydrogen was fed into the reactor together with ethyleneuntil the total pressure was 28 bar. Polymerization was carried out forone hour and the total pressure was maintained constant by means ofethylene feeding.

Copolymerization was carried out in a corresponding manner by adding 180g of 1-butene before the feeding in of ethylene.

                  TABLE 1                                                         ______________________________________                                        Polymerization results                                                               Activity                                                                      g PE/g   g PE/g   MI    MI    MFR                                      Example                                                                              cat      Ti       (21.6)                                                                              (2.16)                                                                              (21/2)                                                                              BD                                 ______________________________________                                        1      12100    302500   18.3  0.59  30.9  0.39                               2      10350    260000   54.9  1.71  32.1  0.34                               3      8150     177000   12.7  0.40  32.0  0.30                               4      5440     286000   9.70  0.32  30.6  0.29                                4*    7110     374000   62.9  2.50  25.2  0.31                               ______________________________________                                         MI: Melt Index, ASTM D 1238, condition 190° C./21.6 kg and 2.16 kg     MFR: Melt Flow Ratio, melt indices 21.6 and 2.16 kg                           BD: Bulk Density, g/ml                                                        *copolymerization with 1butene                                           

We claim:
 1. A method for the preparation of a solid procatalyst composition for a catalyst system intended for the polymerization of olefins, comprising the steps of:(i) silanating a support material with an organic silicon compound; (ii) subjecting the resulting silanated support material to an impregnation treatment with a magnesium halide and a monocarboxylic acid alkyl ester which dissolves or disperses said halide; (iii) reacting the impregnated support material with an organometallic compound of a metal of Group IA-IIIA or a silicon compound selected from the group consisting of halide silicon compounds and alkyl halide silicon compounds; and (iv) treating said support material with a transition metal compound.
 2. A method according to claim 1, wherein said organic silicon compound of step (i) is hexamethyldisilazane.
 3. A method according to claim 1, wherein said support material is silica.
 4. A method according to claim 1, wherein, before the silanation step, a support material which contains hydroxyl groups is kept a temperature below about 200° C., whereby said hydroxyl groups are retained to a substantial degree in said support material until said silanation step.
 5. A method according to claim 4, wherein a support material which contains water is heat-treated before the silanation step at a temperature of about 100°-200° C., whereby the water is removed from said support material but a considerable quantity of hydroxyl groups are retained in it.
 6. A method according to claim 1, wherein said support material is calcined before the silanation step.
 7. A method according to claim 1, wherein said magnesium halide is dissolved or slurried in said ester, and said support material is impregnated with the obtained solution or slurry.
 8. A method according to claim 1, wherein said magnesium halide is anhydrous magnesium chloride and wherein said monocarboxylic acid alkyl ester is ethyl acetate.
 9. A method according to claim 1, wherein said impregnated support material is reacted in step (iii) with an aluminum alkyl compound and is treated in step (iv) with a titanium halogen compound.
 10. A method according to claim 9, wherein said aluminum alkyl compound of step (iii) is triethylaluminum and said titanium halogen compound of step (iv) is titanium tetrachloride.
 11. A solid procatalyst composition for a catalyst system intended for the polymerization of olefins, prepared by the method according to any one of claims 1-9 or
 10. 